1. Field of the Invention
The present invention pertains generally to compressors and, more particularly, relates to compressors provided with a discharge muffler in a discharge passage.
2. Description of the Related Art
It is known that some conventional compressors, including variable displacement compressors, are provided with an expansion-type discharge muffler in a discharge passage for reducing vibrations and acoustic noise generated when the compressors are in operation. The cross-sectional area of a discharge gas passage is enlarged and then reduced in a muffling space formed in the discharge muffler. Discharge gas pressure pulsations are damped in the discharge muffler by causing reflection and interference in its muffling space. Since the discharge gas pressure pulsations are damped in this manner, it is possible to prevent vibrations and acoustic noise which could occur in an external refrigerant circuit due to the pressure pulsations.
In another type of compressor previously proposed, it is provided with a check valve located downstream of a discharge muffler, in which a discharge passage is blocked by the check valve when the compressor is not in operation. In this construction, a high-pressure discharge gas is prohibited from flowing back into the discharge muffler and the compressor from an external refrigerant circuit connected to the discharge passage of the compressor, making it possible to prevent an excessive amount of high-pressure discharge gas from being fed back into the compressor, when it is not in operation.
A conventional compressor employing the aforementioned arrangement, however, would still produce discharge gas pressure pulsations when a valve element of its check valve begins to hunt, and such pressure pulsations are likely to cause the external refrigerant circuit to generate vibrations and acoustic noise. This is mainly because the check valve is provided downstream of the discharge muffler in the discharge passage.
Another problem of the conventional arrangement in which the check valve is provided downstream of the discharge muffler is that the high-pressure discharge gas upstream of the check valve as well as the volumetric capacity of the discharge muffler flows back into a crankcase of the compressor when the compressor is not in operation. This results in an excessive increase in the internal pressure of the crankcase and produces an adverse effect on the durability of a lip-type seal mounted on a rotary shaft of the compressor.